It is all about budget and estimated return in the end. If a developer pays a freelancer to make pixelart they will have a certain budget limit of how much they can shell out. The pixel artist then can say, OK, I can do this, and this will be about the standard of work I can do, if you want me to go super fancy it will come out more expensive. It is as simple as that. Pixelart is a lot of work, and if you had an AAA sized team work on a pixelart game with something like 30 of the best pixelartists, a brilliant art director and great programmers and all that, and of course a good concept, you could make something totally amazing as far as art goes. But it is very unlikely to happen because it would be a very high risk investment that no publisher at this point in time will be willing to make.
Then you got something like kickstarter, but even that wont allow for something of this scope. A lot of the goals on there are unrealistically low to begin with.